1. Field of Invention
The present invention relates to a field of vacuum electronic technology, and more particularly to a sub-wavelength miniaturized all-metal slow-wave structure based on electric resonance, which is a high frequency part of a traveling-wave tube or a backward wave tube operating in the centimeter wave and millimeter wave bands, and has a high power capacity. Under a same operating condition, a sectional area of the slow-wave structure is only 35-50% of a conventional slow-wave structure.
2. Description of Related Arts
There are some advantages such as high power and high efficiency for vacuum electron devices, which play an important role on large scientific devices of electronic science and technology fields such as communication, radar, guidance, electronic countermeasure, microwave heating, accelerator and controlled thermonuclear fusion. With the rapid development of semiconductor power devices, vacuum electron devices such as traveling-wave tube face enormous challenges in communication, radar, etc. Because of high efficiency, large power and strong resistance to various radiations from outer space, space traveling-wave tube is one of the heart devices of satellite communication. However, how to reduce volume and weight thereof and how to further improve electron efficiency are the major problems. In addition, vacuum electron devices with small volume and high power are badly needed as a radiation source for electronic interference; and power source with continuous wave, high power and small volume is needed for microwave heating. Slow-wave structure is one of the core components of traveling-wave tube and backward wave tube. Due to the interaction of electron beam and electromagnetic wave in the slow-wave structure, the kinetic energy of the electron beam is transformed into high power microwave or millimeter wave for being outputted. Conventionally, the slow-wave structures commonly used comprises helix, coupled-cavity, meandering waveguide and rectangular grid slow-wave structure, and the most widely used slow-wave structures are helix and the coupled-cavity slow-wave structures.
Conventionally, because of a wide band, the helix traveling-wave tube is the most widely used one. However, because the coupling impedance thereof is relatively low, the output power is limited, which means the conventional helix traveling wave tube belongs to a medium or small power amplifier. For example, coupling impedance of the helix traveling-wave tube operating at S band is 100-200 ohms. Because dielectric material is loaded, inner heat is difficult to be transferred outside, and the helix traveling-wave tube is easy to be broken by high heat. Therefore the power capacity is small. The coupled-cavity traveling-wave tube is an all-metal slow-wave device with high power capacity, which is an amplifier with the highest power output compared with other traveling-wave tubes at present. Coupling impedance thereof at S band is 300-400 ohms. However, because of a complex structure, the coupled-cavity traveling-wave tube is difficult to be assembled and is not conducive to mass production. According to working principles of the traveling-wave tubes, the maximum output power is in proportion to ⅓-power of the coupling impedance. Therefore, improving the coupling impedance is one of the effective methods for improving output power and efficiency of the traveling-wave tube, and improving the coupling impedance is actually enhancing longitudinal electric field intensity in the slow-wave structure.
In 1996, Pendry et al. from Imperial College London utilized a metal rod array with certain periodic for forming an effective medium whose effective permittivity has a negative real part (J. B. Pendry, A. J. Holden, W. J. Stewart, and I. Youngs. Extremely low frequency plasmons in metallic mesostructures. Phys. Rev. Lett., Vol. 76, 4773-4776, 1996). In 2005, based on the theory of Pendry et al., Spanish scholars Esteban et al. loaded two-dimensional metal rods (generally formed by copper) into a rectangular waveguide operating at a cutoff frequency, which illustrates by principle that the waveguide is also able to spread quasi-TM waves (J. Esteban, C. Camacho-Penalosa, J. E. Page, T. M. Martin-Guerrero, and E. Marquez-Segura. Simulation of negative permittivity and negative permeability by means of evanescent waveguide modes-theory and experiment. IEEE Trans. Microwave Theory Tech., Vol. 53, No. 4, 1506-1514, 2005). However, electron beam channel is not able to be well formed in the rectangular waveguide loaded with the artificial electromagnetic medium, and electron efficiency thereof is low. As a result, the structure is not applicable in vacuum electronic devices.